Pain, nerve dysfunction and fatigue in a vibration-exposed population

Brain mechanisms of pain relief by transcutaneous electrical nerve stimulation: A functional magnetic resonance imaging study

BACKGROUND

Although the exact mechanism of TENS pain relief is unknown, it is believed that TENS impulses interrupt nociceptive signals at the dorsal horn of the spinal cord.

AIMS

To evaluate the hypotheses that during pain caused by noxious stimuli, brain responses, temporal summation and brain functional connectivity are modulated by TENS, and that mechanisms of pain relief by TENS differ between men and women.

METHODS

During fMRI scanning, the same noxious stimuli were delivered to each participant in pain-only and pain+TENS conditions. In the pain-only condition, noxious stimuli were presented without TENS. In the pain+TENS condition, participants received noxious stimuli and TENS concurrently. Participants were initially presented with TENS at an intensity that was just below that causing discomfort. TENS intensity was presented in a step-wise fashion to prevent temporal summation from repetitive noxious stimuli.

RESULTS

Pain and unpleasantness ratings were significantly higher in the pain-only than the pain+TENS condition. With non-painful TENS, primary and secondary somatosensory and parietal cortices were activated, and temporal summation from repetitive noxious stimuli was prevented. Periaqueductal gray (PAG) and lateral prefrontal cortex functional connectivity was increased by TENS, and modulated by testosterone and cortisol. Women reported greater pain during TENS than men, and showed greater activation in the temporoparietal junction cortex and increased PAG functional connectivity with the orbitofrontal cortex.

CONCLUSION

TENS led to pain reduction, probably due to activation of the descending pain-inhibitory pathway, indicating that this TENS method may be applied in clinical practice.

Heavy snorer's disease: a progressive local neuropathy

"Heavy snorer's disease" is defined as progression from heavy snoring to obstructive sleep apnoea syndrome (OSAS). Apart from significant weight gain, the aetiology underlying progression to a collapse of the upper airways during inspiration and sleep remains unclear. Previous studies have shown that nocturnal respiratory disturbances became worse, even in some OSAS patients who did not gain weight. The patency of the upper airways depends on the balance between the negative intrapharyngeal pressure developed during inspiration and its counteraction by dilating muscles. The reflexogenic dilation is probably mediated by afferent nerve endings in the pharyngeal mucosa. Chronic vibration of a tissue may cause neuronal damage. Therefore, the hypothesis that snoring per se might cause progressive pharyngeal nerve lesion has been tested in a series of studies from the Karolinska Institute, Stockholm, which, along with other studies, will be reviewed here. In these studies it was found that a majority of patients with heavy snoring and different degrees of respiratory disturbance had signs of pharyngeal afferent and efferent (motor) nerve lesions. These lesions may cause the collapse of upper airways in OSAS. Since it is not known which "heavy snorer" will develop OSAS, early effective prevention and or treatment of snoring is called for.

Meta-analysis of published studies of work-related carpal tunnel syndrome

The published information about work-related carpal tunnel syndrome (CTS) was surveyed to identify risk estimates and possible biases influencing the risk estimates. Seventeen studies from the English-language literature were identified and study characteristics were coded for univariate and regression analysis. Country of publication, study population, force, and repetitive motion were significant predictors or risk, with R(2) = 0.57, adjusted R(2) = 0.43, Cp = 5.79, and AIC = 19.6 using the best-subset method of variable selection. Using the forward-variable selection method, country, study population, study type, and repetitive motion were significant predictors, with R(2) = 0.57, Cp = 6.24, p = 0.033. Excess risks of work-related CTS were consistent in the studies reviewed. Studies published in the United States reported higher risk estimates than did those published elsewhere. Some industrial populations were found to have higher risk estimates than others. Cross-sectional designs were the most common epidemiologic approach, but are not without methodologic concerns.

Clinical applications of quantitative sensory testing (QST)

Quantitative sensory testing (QST) has been used clinically for the last two decades, yielding a substantial number of publications regarding these applications. In this review we tried to amass together the major findings of these publications into one monograph, excluding those dealing with pain. This was done with the aim of assisting clinicians in the better use of QST techniques for the benefit of their patients.